Method and apparatus for transmitting data in wireless lan system

ABSTRACT

Disclosed are a method and an apparatus for transmitting data in a wireless LAN system. The method for transmitting data comprises the steps of: generating a master-beacon frame including identifier information of an end-point terminal connected to a relay device; and transmitting the master-beacon frame. As a result, the occurrence of a buffer overflow in the relay device can be prevented.

TECHNICAL FIELD

The present invention generally relates to data transmission technologyin a wireless local area network (WLAN) system and, more particularly,to a method and apparatus for transmitting data to an end terminal in aWLAN system including a relay device.

BACKGROUND ART

With the development of information and communication technology,various wireless communication technologies have been developed. Amongthese technologies, a wireless local area network (WLAN) denotestechnology for allowing wireless access to the Internet in homes,businesses or specific service areas using a mobile terminal such as apersonal digital assistant (PDA), a laptop computer, a portablemultimedia player (PMP), a smart phone, or a tablet PC, based on radiofrequency (RF) technology.

Standards for WLAN technology have been developed as Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standards. WLANtechnology conforming to the IEEE 802.11a standard is operated based onan orthogonal frequency division multiplexing (OFDM) scheme, and iscapable of providing a maximum data rate of 54 Mbps in a 5 GHz band.WLAN technology conforming to the IEEE 802.11b standard is operatedbased on a direct sequence spread spectrum (DSSS) scheme, and is capableof providing a maximum data rate of 11 Mbps in a 2.4 GHz band. WLANtechnology conforming to the IEEE 802.11g standard is operated based onthe OFDM or DSSS scheme, and is capable of providing a maximum data rateof 54 Mbps in a 2.4 GHz band.

WLAN technology conforming to the IEEE 802.11n standard is operatedbased on the OFDM scheme in a 2.4 GHz band and a 5 GHz band, and iscapable of providing a maximum data rate of 300 Mbps for four spatialstreams when a Multiple-Input Multiple-Output OFDM (MIMO-OFDM) scheme isused. WLAN technology conforming to the IEEE 802.11n standard maysupport a channel bandwidth of up to 40 MHz and is capable of providinga maximum data rate of 600 Mbps in that case.

As the popularization of such WLAN technology has been activated andapplications using WLANs have been diversified, the requirement for newWLAN technology that supports throughput higher than that of existingWLAN technology is increasing. Very high throughput (VHT) WLANtechnology is proposed technology that supports a data rate of 1 Gbps ormore. Meanwhile, in a system based on such WLAN technology, a problemarises in that, as the distance between WLAN devices increases,communication efficiency is deteriorated.

DISCLOSURE Technical Problem

An object of the present invention to solve the above problems is toprovide a data transmission method for improving the efficiency of aWLAN system.

Another object of the present invention to solve the above problems isto provide a data transmission apparatus for improving the efficiency ofa WLAN system.

Technical Solution

In accordance with an embodiment of the present invention to accomplishthe above objects, a communication system based on WLAN technologyincludes a certain terminal acting as a relay device that relays datatransmitted between a master access point and an end terminal.

Here, a data transmission method performed by a master access pointaccording to an embodiment of the present invention includes generatinga master beacon frame including identifier information of an endterminal connected to the relay device, and transmitting the masterbeacon frame.

Here, the master beacon frame may include a relay traffic indication map(RTIM) having both identifier information of the relay device and theidentifier information of the end terminal.

Here, the RTIM may include identifier information of multiple relaydevices and identifier information of at least one end terminalconnected to each of the relay devices.

Here, the identifier information may be an association identifier (AID).

Here, the data transmission method may further include receiving anacknowledge (ACK) frame from the relay device having received the masterbeacon frame, transmitting a data frame buffered for the end terminal tothe relay device, and receiving a response frame, as a response to thedata frame, from the relay device.

Here, the response frame may be an ACK frame.

Here, the response frame may be a data frame.

A data transmission method performed by a relay device according to anembodiment of the present invention includes receiving, from a masteraccess point, a master beacon frame including identifier information ofan end terminal connected to the relay device, generating a trafficindication map (TIM) including the identifier information of the endterminal, and transmitting a relay beacon frame including the TIM.

Here, the master beacon frame may include a relay traffic indication map(RTIM) having both identifier information of the relay device and theidentifier information of the end terminal.

Here, the RTIM may include identifier information of multiple relaydevices and identifier information of at least one end terminalconnected to each of the relay devices.

Here, the identifier information may be an association identifier (AID).

Here, the data transmission method may further include receiving a powersave (PS)-Poll frame or a trigger frame from the end terminal havingreceived the relay beacon frame, transmitting an ACK frame as a responseto the PS-Poll frame or the trigger frame, and receiving a data framebuffered for the end terminal from the master access point.

Here, the data transmission method may further include transmitting anACK frame as a response to the data frame, transmitting the data frameto the end terminal, and receiving an ACK frame as a response to thedata frame from the end terminal.

Here, the data transmission method may further include transmitting thedata frame to the end terminal, and receiving an ACK frame as a responseto the data frame from the end terminal.

Advantageous Effects

In accordance with the present invention, the wireless transmissionefficiency of a WLAN system can be improved.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an embodiment of a station forperforming methods according to the present invention;

FIG. 2 is a conceptual diagram showing an embodiment of theconfiguration of a WLAN system conforming to IEEE 802.11;

FIG. 3 is a flowchart showing a terminal association procedure in aninfrastructure BSS;

FIG. 4 is a conceptual diagram showing the infrastructure BSS of a WLANsystem;

FIG. 5 is a block diagram showing an embodiment of a hierarchical AIDstructure;

FIG. 6 is a block diagram showing an embodiment of the structure of aTIM information element (IE);

FIG. 7 is a block diagram showing an embodiment of the structure of aTIM encoded on a block basis;

FIG. 8 is a flow diagram showing an embodiment of a datatransmission/reception procedure;

FIG. 9 is a conceptual diagram showing a WLAN system including relaydevices;

FIG. 10 is a block diagram showing the logical configuration of a relaydevice;

FIG. 11 is a conceptual diagram showing a data transmission method in aWLAN system including a relay device;

FIG. 12 is a flowchart showing a data transmission method in a WLANsystem including a relay device according to an embodiment of thepresent invention;

FIG. 13 is a conceptual diagram showing a data transmission method in aWLAN system including a relay device according to an embodiment of thepresent invention;

FIG. 14 is a conceptual diagram showing a relay traffic indication map(RTIM) according to an embodiment of the present invention; and

FIG. 15 is a conceptual diagram showing a data transmission method in aWLAN system including a relay device according to another embodiment ofthe present invention.

BEST MODE

The present invention may be variously changed and may have variousembodiments, and specific embodiments will be described in detail belowwith reference to the attached drawings.

However, it should be understood that those embodiments are not intendedto limit the present invention to specific disclosure forms and theyinclude all changes, equivalents or modifications included in the spiritand scope of the present invention.

The terms such as “first” and “second” may be used to describe variouscomponents, but those components should not be limited by the terms. Theterms are merely used to distinguish one component from othercomponents. A first component may be designated as a second componentand a second component may be designated as a first component in thesimilar manner, without departing from the scope based on the concept ofthe present invention. The term “and/or” includes a combination of aplurality of related items or any of the plurality of related items.

It should be understood that a representation indicating that a firstcomponent is “connected” or “coupled” to a second component may includethe case where the first component is connected or coupled to the secondcomponent with some other component interposed therebetween, as well asthe case where the first component is “directly connected” or “directlycoupled” to the second component. In contrast, it should be understoodthat a representation indicating that a first component is “directlyconnected” or “directly coupled” to a second component means that nocomponent is interposed between the first and second components.

The terms used in the present specification are merely used to describespecific embodiments and are not intended to limit the presentinvention. A singular expression includes a plural expression unless adescription to the contrary is specifically pointed out in context. Inthe present specification, it should be understood that the terms suchas “include” or “have” are merely intended to indicate that features,numbers, steps, operations, components, parts, or combinations thereofare present, and are not intended to exclude a possibility that one ormore other features, numbers, steps, operations, components, parts, orcombinations thereof will be present or added.

Unless differently defined, all terms used here including technical orscientific terms have the same meanings as the terms generallyunderstood by those skilled in the art to which the present inventionpertains. The terms identical to those defined in generally useddictionaries should be interpreted as having meanings identical tocontextual meanings of the related art, and are not interpreted as beingideal or excessively formal meanings unless they are definitely definedin the present specification.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the attached drawings. For easyunderstanding of the entire part of the invention in the followingdescription of the present invention, the same reference numerals areused to designate the same or similar elements throughout the drawings,and repeated descriptions of the same components will be omitted.

Throughout the present specification, a station (STA) denotes anyfunctional medium that includes medium access control (MAC) conformingto the IEEE 802.11 standards and a physical layer interface for awireless medium. Stations may be classified into a station (STA) that isan access point (AP) and a station (STA) that is a non-AP. The stationthat is an AP may be simply called an access point (AP), and the stationthat is a non-AP may be simply called a terminal.

A ‘station (STA)’ may include a processor and a transceiver, and mayfurther include a user interface, a display device, etc. The processordenotes a unit devised to generate a frame to be transmitted over awireless network or process a frame received over the wireless network,and may perform various functions to control the station (STA). Thetransceiver denotes a unit that is functionally connected to theprocessor and is devised to transmit and receive a frame over thewireless network for the station (STA).

An ‘access Point (AP)’ may denote a centralized controller, a basestation (BS), a radio access station, a Node B, an evolved Node B, arelay, a Mobile Multihop Relay (MMR)-BS, a Base Transceiver System(BTS), a site controller, etc., and may include some or all of thefunctions thereof.

A ‘terminal (i.e. non-AP)’ may denote a Wireless Transmit/Receive Unit(WTRU), User Equipment (UE), a User Terminal (UT), an Access Terminal(AT), a Mobile Station (MS), a mobile terminal, a subscriber unit, aSubscriber Station (SS), a wireless device, a mobile subscriber unit,etc., and may include some or all of the functions thereof.

Here, the terminal may denote a desktop computer capable ofcommunication, a laptop computer, a tablet PC, a wireless phone, amobile phone, a smart phone, a smart watch, smart glasses, an e-bookreader, a Portable Multimedia Player (PMP), a portable game console, anavigation device, a digital camera, a Digital Multimedia Broadcasting(DMB) player, a digital audio recorder, a digital audio player, adigital picture recorder, a digital picture player, a digital videorecorder, a digital video player, etc.

FIG. 1 is a block diagram showing an embodiment of a station forperforming methods according to the present invention.

Referring to FIG. 1, a station 10 may include at least one processor 11,memory 12, and a network interface device 13 connected to a network 20and configured to perform communication. The station 10 may furtherinclude an input interface device 14, an output interface device 15, anda storage device 16. The components included in the station 10 may beconnected to each other through a bus 17, and may then performcommunication with each other.

The processor 11 may execute program instructions stored in the memory12 and/or the storage device 16. The processor 11 may denote a centralprocessing unit (CPU), a graphics processing unit (GPU), or an exclusiveprocessor for performing the methods according to the present invention.Each of the memory 12 and the storage device 16 may be implemented as avolatile storage medium and/or a nonvolatile storage medium. Forexample, the memory 12 may be implemented as read only memory (ROM)and/or random access memory (RAM).

The embodiments of the present invention are applied to a WLAN systemconforming to the IEEE 802.11 standards, and may also be applied toother communication systems as well as the WLAN system conforming to theIEEE 802.11 standards.

For example, the embodiments of the present invention may be applied tothe mobile Internet such as a Wireless Personal Area Network (WPAN), aWireless Body Area Network (WBAN), Wireless Broadband Internet (WiBro),or Worldwide Interoperability for Microwave Access (Wimax), a secondgeneration (2G) mobile communication network such as a Global System forMobile communication (GSM) or Code Division Multiple Access (CDMA), a 3Gmobile communication network such as Wideband Code Division MultipleAccess (WCDMA) or CDMA2000, a 3.5G mobile communication network such asHigh-Speed Downlink Packet Access (HSDPA) or High-Speed Uplink PacketAccess (HSUPA), a 4G mobile communication network such as Long-TermEvolution (LTE) or LTE-Advanced, or a 5G mobile communication network.

FIG. 2 is a conceptual diagram showing an embodiment of theconfiguration of a WLAN system conforming to IEEE 802.11.

Referring to FIG. 2, the WLAN system conforming to IEEE 802.11 mayinclude at least one basic service set (BSS). The BSS denotes a set ofstations (STA 1, STA 2(AP 1), STA 3, STA 4, STA 5(AP 2), STA 6, STA 7,STA 8) which are successfully synchronized with each other and arecapable of communicating with each other, and is not a concept meaning aspecific area.

BSSs may be classified into an infrastructure BSS and an independent BSS(IBSS). Here, BSS 1 and BSS 2 denote infrastructure BSSs and BSS 3denotes an IBSS.

BSS 1 may include a first terminal STA 1, a first access point STA 2 (AP1) for providing a distribution service, and a distribution system (DS)for connecting multiple access points STA 2(AP 1) and STA 5(AP 2) toeach other. In BSS 1, the first access point STA 2 (AP 1) may manage thefirst terminal STA 1.

BSS 2 may include a third terminal STA 3, a fourth terminal STA 4, asecond access point STA 5 (AP 2)) for providing a distribution service,and a distribution system (DS) for connecting the multiple access pointsSTA 2(AP 1) and STA 5(AP 2) to each other. In the BSS 2, the secondaccess point STA 5 (AP 2) may manage the third terminal STA 3 and thefourth terminal STA 4.

BSS 3 denotes an IBSS operating in an ad-hoc mode. In the BSS 3, thereis no access point that functions as a centralized management entity.That is, in the BSS 3, terminals STA 6, STA 7, and STA 8 are managed ina distributed manner. In the BSS 3, all of the terminals STA 6, STA 7,and STA 8 may denote mobile terminals, and access to the distributionsystem (DS) is not permitted, thus constituting a self-containednetwork.

The access points STA 2(AP 1) and STA 5(AP 2) may provide access to thedistribution system (DS) via a wireless medium for the terminals STA 1,STA 3, and STA 4 connected thereto. Communication between the terminalsSTA 1, STA 3, and STA 4 in the BSS 1 or BSS 2 is generally performed viathe access point STA 2 (AP 1) or STA 5 (AP 2), but direct communicationmay be performed between the terminals STA 1, STA 3, and STA 4 when adirect link is set up therebetween.

Multiple infrastructure BSSs may be connected to each other through thedistribution system (DS). The multiple BSSs connected through thedistribution system (DS) are called an extended service set (ESS). Theentities included in the ESS, that is, STA 1, STA 2(AP 1), STA 3, STA 4,and STA 5(AP 2), are capable of communicating with each other, and anyterminal STA 1, STA 3, or STA 4 may move from a single BSS to anotherBSS while performing seamless communication in the same ESS.

The distribution system (DS) is a mechanism for allowing one accesspoint to communicate with another access point. In accordance with theDS, the access point may transmit frames for terminals coupled to a BSSmanaged thereby, or may transmit frames for any terminal that has movedto another BSS. Further, the access point may transmit and receiveframes to and from an external network, such as a wired network. Such aDS is not necessarily a network and is not limited in its form as longas it is capable of providing a predetermined distribution servicedefined in the IEEE 802.11 standards. For example, the distributionsystem may be a wireless network such as a mesh network, or a physicalstructure for connecting the access points to each other.

Each terminal (STA) in the infrastructure BSS may be associated with anaccess point (AP). When associated with the access point (AP), theterminal (STA) may transmit and receive data.

FIG. 3 is a flowchart showing a terminal association procedure performedin an infrastructure BSS.

Referring to FIG. 3, the STA association procedure performed in theinfrastructure IBSS may be chiefly divided into the step of probing anAP (probe step), the step of performing authentication with the probedAP (authentication step), and the step of associating with the AP withwhich authentication has been performed (association step).

The terminal (STA) may first probe neighboring APs using a passivescanning method or an active scanning method. When the passive scanningmethod is used, the terminal (STA) may probe neighboring APs byoverhearing the beacons transmitted from the APs. When the activescanning method is used, the STA may probe neighboring APs bytransmitting a probe request frame and receiving a probe response framewhich is a response to the probe request frame from the APs.

When neighboring APs are detected, the STA may perform the step ofperforming authentication with each detected AP. In this case, the STAmay perform the step of performing authentication with multiple APs.Authentication algorithms conforming to the IEEE 802.11 standards may beclassified into an open system algorithm for exchanging twoauthentication frames with each other and a shared key algorithm forexchanging four authentication frames with each other.

Based on the authentication algorithms conforming to the IEEE 802.11standards, the STA may transmit an authentication request frame andreceive an authentication response frame, which is a response to theauthentication request frame, from each AP, thus completingauthentication with each AP.

When authentication has been completed, the STA may perform the step ofassociating with the AP. In this case, the STA may select a single APfrom among the APs with which authentication has been performed, and mayperform the step of associating with the selected AP. That is, the STAmay transmit an association request frame to the selected AP and receivean association response frame, which is a response to the associationrequest frame, from the selected AP, thus completing association withthe selected AP.

The WLAN system denotes a local area network in which multiplecommunication entities conforming to the IEEE 802.11 standards mayexchange data with each other in a wirelessly connected state.

FIG. 4 is a conceptual diagram showing the infrastructure BSS of a WLANsystem.

Referring to FIG. 4, the infrastructure BSS may include a single accesspoint (AP) and multiple terminals STA 1 and STA 2. The AP may transmit abeacon frame including a service set ID (SSID), which is a uniqueidentifier, in a broadcast manner. The beacon frame may provideinformation about the presence and association of the AP to terminalsthat are not associated with the AP, and may notify the terminalsassociated with the AP of the presence of data that is transmitted to aspecific terminal.

Each terminal that is not associated with the AP may probe the AP usinga passive scanning method or an active scanning method, and may acquireassociation information from the probed AP. In the case of the passivescanning method, the terminal may probe the AP by receiving a beaconframe from the AP. In the case of the active scanning method, theterminal may probe the AP by transmitting a probe request frame andreceiving a probe response frame, which is a response thereto, from theAP.

Each terminal that is not associated with the AP may attempt to performauthentication with a specific AP based on association informationacquired from the beacon frame or the probe response frame. A terminalthat has succeeded in authentication may transmit an association requestframe to the corresponding AP, and the AP, having received theassociation request frame, may transmit an association response frameincluding the AID of the terminal to the terminal. Via the aboveprocedure, the terminal may be associated with the AP.

FIG. 5 is a block diagram showing an embodiment of a hierarchical AIDstructure.

Referring to FIG. 5, in the IEEE 802.11 standards, an AID having ahierarchical structure may be used to efficiently manage multipleterminals. An AID assigned to a single terminal may be composed of apage ID, a block index, a sub-block index, and a terminal index (STAindex). The group to which the terminal belongs (i.e. a page group, ablock group, or a sub-block group) may be identified using informationabout individual fields.

FIG. 6 is a block diagram showing an embodiment of the structure of atraffic indication map (TIM) information element (IE).

Referring to FIG. 6, the TIM IE may include an element ID field, alength field, a delivery traffic indication message (DTIM) count field,a DTIM period field, a bitmap control field, and a partial virtualbitmap field. That is, the TIM IE includes information required toindicate a bit corresponding to the AID of a terminal when data to betransmitted to the terminal is buffered in the AP, and this informationmay be encoded into the bitmap control field and the partial virtualbitmap field.

FIG. 7 is a block diagram showing an embodiment of the structure of aTIM encoded on a block basis.

Referring to FIG. 7, in the IEEE 802.11 standards, the TIM may beencoded on a block basis. A single encoding block may include a blockcontrol field, a block offset field, a block bitmap field, and at leastone sub-block field.

The block control field may denote the encoding mode of the TIM. Thatis, the block control field may represent a block bitmap mode, a singleAID mode, an offset+length+bitmap (OLB) mode, or an inverse bitmap mode.The block offset field may represent the offset of an encoded block. Theblock bitmap field may represent a bitmap indicating the location of thesub-block in which an AID bit is set. The sub-block bitmap field mayrepresent a bitmap indicating the location of an AID in the sub-block.

FIG. 8 is a flow diagram showing an embodiment of a datatransmission/reception procedure.

Referring to FIG. 8, an access point (AP) may transmit a beacon frameincluding a TIM IE in a broadcast manner. A terminal (STA) operating ina power save mode may be awakened at intervals of a beacon period, inwhich a DTIM count becomes 0, and may receive a beacon frame. Theterminal (STA) is configured to, when a bit corresponding to its AID isset to ‘1’ in the TIM included in the received beacon frame, transmit apower save (PS)-Poll frame to the AP, thus notifying the AP that the STAis ready to receive data. Upon receiving the PS-Poll frame, the AP maytransmit a data frame to the corresponding STA.

In the WLAN system, communication entities (i.e. access points,terminals, etc.) share a wireless channel and contend with otherentities to access the wireless channel based on a carrier sensemultiple access (CSMA)/collision avoidance (CA) scheme. First, eachcommunication entity may check the occupied state of the wirelesschannel using a physical channel sensing scheme and a virtual channelsensing scheme before accessing the wireless channel.

The physical channel sensing scheme may be implemented via channelsensing, which detects whether energy of a predetermined level or moreis present in the wireless channel. When energy of a predetermined levelor more is detected using the physical channel sensing scheme, theterminal may determine that the wireless channel is occupied by anotherterminal, and thus may perform again channel sensing after waiting for arandom backoff time. Meanwhile, when energy of less than a predeterminedlevel is detected using the physical channel sensing scheme, theterminal may determine that the wireless channel is in an idle state,and may then access the corresponding wireless channel and transmit asignal through the wireless channel.

The virtual channel sensing scheme may be implemented by setting apredicted channel occupation time using a network allocation vector(NAV) timer. In the WLAN system, upon transmitting a frame, acommunication entity may write the time required to complete thetransmission of the corresponding frame in the duration field of theheader of the frame. When normally receiving a certain frame through thewireless channel, the communication entity may set its own NAV timerbased on a value in the duration field of the header of the receivedframe. When receiving a new frame before the NAV timer has expired, thecommunication entity may update the NAV timer based on the value in theduration field of the header of the newly received frame. When the NAVtimer has expired, the communication entity may determine that theoccupation of the wireless channel has been released, and may thencontend for access to a wireless channel.

The communication entity may support multiple data rates of a physicallayer depending on various modulation schemes and various channel codingrates. Generally, a high data rate for the physical layer enables alarge amount of data to be transmitted during a short wireless channeloccupation time, but requires high signal quality. In contrast, a lowdata rate for the physical layer enables data to be transmitted even atlow signal quality, but requires a relatively long wireless channeloccupation time.

Since the resources of the wireless channel are shared betweencommunication entities, the overall capacity of the WLAN system may beincreased only when the maximum amount of data is transmitted during thetime for which a specific communication entity occupies the wirelesschannel. That is, the overall capacity of the WLAN system may beincreased when the terminal transmits and receives data to and from theAP at the highest possible data rate for the physical layer. The highestdata rate for the physical layer may be realized when signal quality issufficiently secured owing to a short distance between the AP and theterminal. If the terminals are located far away from the AP, the datarate of the physical layer becomes low, thus resulting in the reductionof the overall capacity of the WLAN system.

In the WLAN system for providing a communication service to multiplesensor terminals located over a wide area, there may occur the casewhere data cannot be transmitted to the entire area using only thesignal output of a single AP. That is, sensor terminals that cannot besupported with a communication service may be present. Meanwhile, sincea low-power sensor terminal has low signal output, the range in whichthe WLAN system is capable of transmitting uplink data may be furthernarrowed.

In particular, since a terminal located in the coverage boundary of theAP exhibits poor signal quality, the terminal performs communicationwith the AP at a low data rate of the physical layer. Therefore, theoverall capacity of the WLAN system is drastically decreased. Further,when using the low data rate of the physical layer, the low-powerterminal must be awakened for a much longer time in order to transmitthe same amount of data, thus increasing power consumption.

FIG. 9 is a conceptual diagram showing a WLAN system including relaydevices.

Referring to FIG. 9, a master access point (master-AP: M-AP), a firstrelay device R1, a second relay device R2, and a fifth terminal STA 5may constitute a master BSS. The first relay device R1, a first terminalSTA 1, and a second terminal STA 2 may constitute a first relay BSS. Thesecond relay device R2, a third terminal STA 3, and a fourth terminalSTA 4 may constitute a second relay BSS. The relay devices R1 and R2 maybe located at the place where signal quality between the master accesspoint (M-AP) and the terminals STA 1, STA 2, STA 3, and STA 4 isdeteriorated. The first relay device R1 may relay data transmittedbetween the master access point (M-AP) and the first and secondterminals STA 1 and STA 2. The second relay device R2 may relay datatransmitted between the master access point (M-AP) and the third andfourth terminals STA 3 and STA 4. That is, the physical area of themaster access point (M-AP) may be extended via the relay devices R1 andR2.

FIG. 10 is a block diagram showing the logical configuration of a relaydevice.

Referring to FIG. 10, the relay device may include a relay terminal(R-STA), functioning as a master access point (M-AP), and a relay accesspoint (R-AP), functioning as an access point for terminals in anextended area.

The relay terminal (R-STA) may probe the master access point (M-AP) byreceiving a beacon frame or a probe response frame transmitted from themaster access point (M-AP) according to the same procedure as a normalterminal. Thereafter, the relay terminal (R-STA) may sequentiallyperform a procedure for authentication with the probed master accesspoint (M-AP) and a procedure for association with the M-AP.

The relay terminal (R-STA) may relay data transmitted between the masteraccess point (M-AP) and an end terminal. In this case, the relayterminal (R-STA) may relay data that is transmitted using a 4-addressfield. The 4-address field includes a destination address (DA) fieldindicating the address of the final destination of data, a sourceaddress (SA) field indicating the address of the place where the datawas generated, a transmitter address (TA) field indicating the addressof the communication entity that physically transmits a frame containingthe data, and a receiver address (RA) field indicating the address ofthe communication entity that is to physically receive the framecontaining the data.

For example, when desiring to transmit data to an end terminal via arelay device, the master access point (M-AP) may configure and transmitthe header address field of a data frame as follows.

-   -   DA field: address of end terminal    -   SA field: address of master access point (M-AP)    -   TA field: address of master access point (M-AP)    -   RA field: address of relay device

The relay terminal (R-STA) may forward a data frame received from therelay access point (R-AP) to the master access point (M-AP), and mayforward a data frame received from the master access point (M-AP) to therelay access point (R-AP).

When the relay terminal (R-STA) and the master access point (M-AP) areassociated with each other and a transfer path is acquired, the relayaccess point (R-AP) may periodically transmit a beacon frame includingan identifier (SSID) identical to that of the master access point(M-AP). Also, the relay access point (R-AP) may transmit a proberesponse frame in response to a probe request frame from the endterminal, transmit an authentication response frame in response to anauthentication request frame from the end terminal, and transmit anassociation response frame in response to an association request framefrom the end terminal. That is, the relay access point (R-AP) mayperform the same function as the master access point (M-AP).

An end terminal located near the relay device may be connected to arelay-AP (R-AP) located closer to the end terminal than the masteraccess point (M-AP) and may secure high signal quality, thus enablingdata to be transmitted at a high data rate of the physical layer.

The relay access point (R-AP) may generate a beacon frame including anindicator indicating that the R-AP itself is a communication entity forrelaying data transmitted between the master access point (M-AP) and theend terminal, and may transmit the generated beacon frame. Such anindicator may be defined either using one bit in the beacon frame orusing the address field of the master access point (M-AP).

The relay access point (R-AP) may transmit a data frame using a4-address field in the same way as the relay terminal (R-STA).Alternatively, the relay access point (R-AP) may transmit a data frameusing a 3-address field (SA=TA, RA, and DA) when the SA field isidentical to the TA field.

FIG. 11 is a conceptual diagram showing a data transmission method in aWLAN system including a relay device.

Referring to FIG. 11, a master access point (M-AP) and a relay device Rmay constitute a master-BSS (M-BSS), and the relay device R and a firstterminal STA 1 may constitute a relay-BSS (R-BSS). When there is data tobe transmitted to the first terminal STA 1 (i.e. when data for the firstterminal STA 1 is buffered), the master access point (M-AP) may generatea TIM including information about the AID of the relay device Rconnected to the first terminal STA 1. That is, the master access point(M-AP) may set a bit, corresponding to the AID of the relay device R, inthe TIM to ‘1’. The master access point (M-AP) may generate a masterbeacon frame including the TIM, and may transmit the generated masterbeacon frame in a broadcast manner.

The relay device R, having received the master beacon frame, maydetermine that, when its own AID information is included in the TIM ofthe master beacon frame (i.e. when a bit corresponding to its own AID inthe TIM is set to ‘1’), data to be transmitted to the relay device R isbuffered in the master access point (M-AP). The relay device R mayrequest the transmission of data from the master access point (M-AP) bytransmitting a PS-Poll frame (or a trigger frame) thereto. When thePS-Poll frame (or the trigger frame) is received, the master accesspoint (M-AP) may transmit an ACK frame, as a response thereto, to therelay device R, and thereafter may transmit a data frame to the relaydevice R. When the data frame has been successfully received, the relaydevice R may transmit an ACK frame, as a response thereto, to the masteraccess point (M-AP). Meanwhile, since the relay device R is generallyoperated in an awake state, a procedure for transmitting a PS-Poll frame(or a trigger frame) may be omitted. That is, if a preset time (e.g. atime corresponding to short inter-frame space (SIFS)) has elapsed sincethe transmission of a beacon frame, the master access point (M-AP) maytransmit a data frame to the relay device R.

When the data frame received from the master access point (M-AP) is adata frame to be transmitted to the first terminal STA 1, the relaydevice R may generate a TIM including the AID information of the firstterminal STA 1. That is, the relay device R may set a bit, correspondingto the AID of the first terminal STA 1, in the TIM to ‘1’. The relaydevice R may transmit a relay beacon frame including the generated TIMin a broadcast manner.

The first terminal STA 1, having received the relay beacon frame, isconfigured to, when its own AID information is included in the TIM ofthe relay beacon frame (i.e. when a bit corresponding to its own AID inthe TIM is set to ‘1’), recognize that data to be transmitted to the STA1 is buffered in the relay device R. The first terminal STA 1 mayrequest the relay device R to transmit a data frame by transmitting aPS-Poll frame (or a trigger frame) to the relay device R.

When the PS-Poll frame (or the trigger frame) is received, the relaydevice R may transmit an ACK frame, as a response thereto, to the firstterminal STA 1. Thereafter, the relay device R may transmit a data frameto the first terminal STA 1. When the data frame has been successfullyreceived, the first terminal STA 1 may transmit an ACK frame, as aresponse thereto, to the relay device R.

Meanwhile, the first terminal STA 1 connected to the relay device R maybe operated in a power save mode. Therefore, when the first terminal STA1 is in a doze state, the relay device R cannot immediately transmit adata frame to the first terminal STA 1, whereby the transmission of thedata frame is delayed, thus causing an overflow in the buffer of therelay device R. In this case, the relay device R may notify the masteraccess point (M-AP) that no more data frames can be received. Forexample, the relay device R generates an empty data frame in which thepower save mode bit of a control field is set to ‘1’, and transmits theempty data frame to the master access point (M-AP), thus notifying theM-AP that no more data frames can be received.

Generally, the case where the power save mode bit of the control fieldincluded in a frame is set to ‘1’ means that the communication entitythat transmitted the corresponding frame has transitioned to a dozestate. However, since the relay device R is always operated in an awakestate, the master access point (M-AP) may recognize that the residualspace is not present in the buffer of the relay device R when a frame,in which a power save mode bit is set to ‘1’, is received from the relaydevice R. When available space is formed later in the buffer, the relaydevice R may request the master access point (M-AP) to transmit a dataframe by transmitting a PS-Poll frame (or an empty data frame in which apower save mode bit is set to ‘0’) to the master access point (M-AP).

FIG. 12 is a flowchart showing a data transmission method in a WLANsystem including a relay device according to an embodiment of thepresent invention, and FIG. 13 is a conceptual diagram showing a datatransmission method in a WLAN system including a relay device accordingto an embodiment of the present invention.

Referring to FIGS. 12 and 13, a master access point (M-AP) and a relaydevice R may constitute an M-BSS, and the relay device R and a firstterminal STA 1 may constitute an R-BSS. When there is data to betransmitted to the first terminal STA 1 (i.e. when data for the firstterminal STA 1 is buffered), the master access point (M-AP) may generatea relay traffic indication map (RTIM) that includes both the AIDinformation of the first terminal STA 1 and the AID information of therelay device R connected to the first terminal STA 1. That is, themaster access point (M-AP) may set a bit corresponding to the AID of thefirst terminal STA 1 and a bit corresponding to the AID of the relaydevice R in the RTIM to ‘1’.

FIG. 14 is a conceptual diagram showing an RTIM according to anembodiment of the present invention.

Referring to FIG. 14, the RTIM of a master beacon frame may include theAID information of a relay device and the AID information of a terminalconnected to the relay device. Further, the RTIM of the master beaconframe may include pieces of AID information of multiple relay devicesand the AID information of at least one terminal connected to each ofthe relay devices.

Referring back to FIGS. 12 and 13, the master access point (M-AP) maygenerate a master beacon frame including an RTIM, and may transmit thegenerated master beacon frame in a broadcast manner (S100). When themaster beacon frame is received, the relay device R may recognize thatits own AID information and the AID information of the first terminalSTA 1, connected to the relay device R, are included in the RTIM of themaster beacon frame (i.e. a bit corresponding to the AID of the relaydevice R and a bit corresponding to the AID of the first terminal STA 1are set to ‘1’). That is, the relay device R may recognize that data tobe transmitted to the first terminal STA 1 is buffered in the masteraccess point (M-AP).

In this case, the relay device R may generate a TIM including the AIDinformation of the first terminal STA 1. That is, the relay device R maygenerate a TIM in which a bit corresponding to the AID of the firstterminal STA 1 is set to ‘1’. The relay device R may transmit a relaybeacon frame including the TIM in a broadcast manner (S110).

When the relay beacon frame is received, the first terminal STA 1 mayrecognize that its own AID information is included in the TIM of thereceived relay beacon frame (i.e. a bit corresponding to the AID of thefirst terminal STA 1 is set to ‘1’). That is, the first terminal STA 1may recognize that data to be transmitted thereto is buffered in therelay device R. The first terminal STA 1 may request the transmission ofdata from the relay device R by transmitting a PS-Poll frame (or atrigger frame) to the relay device R (S120). Here, the first terminalSTA 1 may indicate that an ACK frame is to be transmitted after thetransmission of the PS-Poll frame (or the trigger frame) by setting theACK indication bit of a signal (SIG) field included in the PS-Poll frame(or the trigger frame) to ‘b00’. Here, the first terminal STA 1 mayrequest the transmission of data by transmitting a separately definedframe, in addition to the PS-Poll frame (or the trigger frame), to therelay device R.

When the PS-Poll frame (or the trigger frame) is received from the firstterminal STA 1, the relay device R may determine that the first terminalSTA 1 has been awakened, and may then transmit an ACK frame as aresponse to the PS-Poll frame (or the trigger frame) (S130). Here, therelay device R may indicate that a data frame is to be transmitted afterthe transmission of the ACK frame by setting the ACK indication bit ofthe SIG field included in the ACK frame to ‘b11’.

Meanwhile, the master access point (M-AP) cannot receive the PS-Pollframe (or the trigger frame) transmitted from the first terminal STA 1,but can receive the ACK frame transmitted from the relay device R as aresponse to the PS-Poll frame (or the trigger frame). Therefore, whenthe ACK frame transmitted from the relay device R is received, themaster access point (M-AP) may determine that the first terminal STA 1has been awakened, and may then transmit a data frame to the relaydevice R (S140). At this time, the master access point (M-AP) mayindicate that an ACK frame is to be transmitted after the transmissionof the data frame by setting the ACK indication field of the SIG fieldincluded in the data frame to ‘b00’.

When the data frame has been successfully received, the relay device Rmay transmit an ACK frame, as a response thereto, to the master accesspoint (M-AP) (S150). Here, the relay device R may indicate that a dataframe is to be transmitted after the transmission of the ACK frame bysetting the ACK indication field of the SIG field included in the ACKframe to ‘b11’.

Thereafter, the relay device R may transmit a data frame to the firstterminal STA 1 (S160). At this time, the relay device R may indicatethat an ACK frame is to be transmitted after the transmission of thedata frame by setting the ACK indication field of the SIG field includedin the data frame to ‘b00’. When the data frame has been successfullyreceived, the first terminal STA 1 may transmit an ACK frame to therelay device R (S170). Here, the first terminal STA 1 may indicate thatno frames are to be transmitted after the transmission of the ACK frameby setting the ACK indication field of the SIG field included in the ACKframe to ‘b10’.

FIG. 15 is a conceptual diagram showing a data transmission method in aWLAN system including a relay device according to another embodiment ofthe present invention.

Referring to FIG. 15, a master access point (M-AP) and a relay device Rmay constitute an M-BSS, and the relay device R and a first terminal STA1 may constitute an R-BSS. Here, a procedure which is performed by theM-AP and which transmits a master beacon frame including an RTIM, aprocedure which is performed by the relay device R and which transmits arelay beacon frame including a TIM, a procedure which is performed bythe first terminal STA 1 and which transmits a PS-Poll frame (or atrigger frame), and a procedure which is performed by the relay device Rand which transmits an ACK frame as a response to the PS-Poll frame (orthe trigger frame) may be identical to those described with reference toFIGS. 12 and 13.

The master access point (M-AP) may determine that the first terminal STA1 has been awakened when receiving an ACK frame from the relay device R.Therefore, the master access point (M-AP) may transmit a data frame,buffered for the first terminal STA 1, to the relay device R. At thistime, the master access point (M-AP) may indicate that a data frame isto be transmitted after the transmission of the data frame by settingthe ACK indication field of the SIG field included in the data frame to‘b11’.

The relay device R, having successfully received the data frame from themaster access point (M-AP), may transmit a data frame to the firstterminal STA 1 without transmitting an ACK frame because the ACKindication field included in the data frame is set to ‘b11’. Here, therelay device R may indicate that an ACK frame is to be transmitted afterthe transmission of the data frame by setting the ACK indication fieldincluded in the data frame to ‘b00’. Meanwhile, when the data frametransmitted from the relay device R is received, the master access point(M-AP) may determine that the data frame previously transmitted therebyhas been successfully received by the relay device R.

When the data frame has been successfully received from the relay deviceR, the first terminal STA 1 may transmit an ACK frame, as a responsethereto, to the relay device R. Here, the first terminal STA 1 mayindicate that no frames are to be transmitted after the transmission ofthe ACK frame by setting the ACK indication field of the SIG fieldincluded in the ACK frame to ‘b10’.

In accordance with the present invention, a master access point mayextend a server area via a relay device. Since a terminal may secure alink having good quality via the relay device, data may be transmittedat high speed. That is, the relay device is used, so that the efficiencyof use of a wireless channel may be improved, and the amount of powerconsumed by the terminal may be reduced.

Further, the master access point may transmit data to a relay deviceonly when an end terminal connected to the relay device is capable ofreceiving data. By means of this, buffer overflows may be prevented fromoccurring in the relay device.

Furthermore, the master access point, the relay device, and the endterminal may minimize channel contention by transmitting frames using anACK indication bit.

Furthermore, the master access point, the relay device, and the endterminal may rapidly transmit and receive data by using a fast datatransmission mode (i.e. omission of an ACK for data).

The embodiments of the present invention may be implemented in the formof program instructions that are executable via various types ofcomputer means, and may be recorded on a computer-readable medium. Thecomputer-readable medium may include program instructions, data files,and data structures solely or in combination. Program instructionsrecorded on the computer-readable medium may have been speciallydesigned and configured for the embodiments of the present invention, ormay be known to or available to those who have ordinary knowledge in thefield of computer software.

Examples of the computer-readable storage medium include all types ofhardware devices specially configured to store and execute programinstructions, such as read only memory (ROM), random access memory(RAM), and flash memory. The hardware devices may be configured tooperate as one or more software modules in order to perform theoperation according to embodiments of the present invention, and viceversa. Examples of the program instructions include machine languagecode, such as code created by a compiler, and high-level language codeexecutable by a computer using an interpreter or the like.

Although the present invention has been described with reference to theembodiments, those skilled in the art will appreciate that the presentinvention can be modified and changed in various forms, withoutdeparting from the spirit and scope of the invention as disclosed in theaccompanying claims.

1. A method for data transmission being performed by a master accesspoint, comprising: generating a master beacon frame including identifierinformation of an end terminal connected to a relay device; andtransmitting the master beacon frame.
 2. The method of claim 1, whereinthe master beacon frame includes a relay traffic indication map (RTIM)having both identifier information of the relay device and theidentifier information of the end terminal.
 3. The method of claim 2,wherein the RTIM includes identifier information of multiple relaydevices and identifier information of at least one end terminalconnected to each of the relay devices.
 4. The method of claim 1,wherein the identifier information is an association identifier (AID).5. The method of claim 1, further comprising: receiving an acknowledge(ACK) frame from the relay device having received the master beaconframe; transmitting a data frame buffered for the end terminal to therelay device; and receiving a response frame, as a response to the dataframe, from the relay device.
 6. The method of claim 5, wherein theresponse frame is an ACK frame.
 7. The method of claim 5, wherein theresponse frame is a data frame.
 8. A method for data transmission beingperformed by a relay device, comprising: receiving, from a master accesspoint, a master beacon frame including identifier information of an endterminal connected to the relay device; generating a traffic indicationmap (TIM) including the identifier information of the end terminal; andtransmitting a relay beacon frame including the TIM.
 9. The method ofclaim 8, wherein the master beacon frame includes a relay trafficindication map (RTIM) having both identifier information of the relaydevice and the identifier information of the end terminal.
 10. Themethod of claim 9, wherein the RTIM includes identifier information ofmultiple relay devices and identifier information of at least one endterminal connected to each of the relay devices.
 11. The method of claim8, wherein the identifier information is an association identifier(AID).
 12. The method of claim 8, further comprising: receiving a powersave (PS)-Poll frame or a trigger frame from the end terminal havingreceived the relay beacon frame; transmitting an ACK frame as a responseto the PS-Poll frame or the trigger frame; and receiving a data framebuffered for the end terminal from the master access point.
 13. Themethod of claim 12, further comprising: transmitting an ACK frame as aresponse to the data frame; transmitting the data frame to the endterminal; and receiving an ACK frame as a response to the data framefrom the end terminal.
 14. The method of claim 12, further comprising:transmitting the data frame to the end terminal; and receiving an ACKframe as a response to the data frame from the end terminal.